The Focus (Focuscript)

### What feature is it?

An XSLT scripting system.

The Focus does with XSLT that which Greasemonkey does with ECMAScript.

Please. Refer to this resource https://git.xmpp-it.net/sch/Focus

### What problem does this feature solve?

It would allow people to utilize any document as RSS, including, yet not limited to, XBEL and FOAF documents.

### Additional description

This is currently tested with project https://git.xmpp-it.net/sch/Slixfeed

Slixfeed only supports The Atom Syndication Format.

With the appropriate Focuscripts, project Slixfeed is able to read other formats such as Atom 0.3, Twtxt, Gemini Feed, JSON, RSS 1.0, RSS 0.9, et cetera.

https://git.xmpp-it.net/sch/Slixfeed/src/branch/master/src/slixfeed/data/focuscript

### This is not a duplicated feature request or new RSS proposal

- [x] I have searched [existing issues](https://github.com/DIYgod/RSSHub/issues) to ensure this feature has not already been requested and this is not a [new RSS proposal](https://github.com/DIYgod/RSSHub/issues/new?assignees=&labels=RSS+proposal&template=rss_request_en.yml).